Normally intervertebral discs, which are located between end plates of adjacent vertebrae, stabilize the spine and distribute forces between the vertebrae and cushion vertebral bodies. The spinal discs may be displaced or damaged due to trauma, disease or aging. A herniated or ruptured annulus fibrosis may result in nerve damage, pain, numbness, muscle weakness, and even paralysis. Furthermore, as a result of the normal aging processes, discs dehydrate and harden, thereby reducing the disc space height and producing instability of the spine and decreased mobility. Most typically surgical correction of a disc space includes a discectomy (surgical removal of a portion or all of the intervertebral disc material.) The discectomy is often followed by fusion of the adjacent vertebrae to alleviate the pain, abnormal joint mechanics, premature development of arthritis, and nerve damage.
Traditional surgical procedures for correction of disc space pathologies can cause significant trauma to the intervening tissues. These open procedures often require a long incision, extensive muscle stripping, prolonged retraction of tissues, denervation and devascularization of tissue. Most of these surgeries require room time of several hours and several weeks of post-operative recovery time due to the use of general anesthesia and the destruction of tissue during the surgical procedure. In some cases, these invasive procedures lead to permanent scarring and pain that can be more severe than the pain leading to the surgical intervention.
One type of open procedure that attempts to minimize trauma to tissue that occurs with an open procedure uses a transforaminal approach to the disc space. This approach is advantageous in that it allows placement of one or more implants into the disc space with a single incision. However, this approach still suffers from the drawback that the posterior musculature and tissue at the surgical site suffer trauma and damage due to the incision and retraction of tissue at the surgical site.
Minimally invasive surgical techniques are particularly desirable for spinal and neurosurgical applications because of the need for access to locations deep within the body and the danger of damage to vital intervening tissues. The development of percutaneous spinal procedures has yielded a major improvement in reducing recovery time and post-operative pain because they require minimal, if any, muscle dissection and they can be performed under local anesthesia. For example, U.S. Pat. No. 4,545,374 to Jacobson discloses a percutaneous lumbar discectomy using a lateral approach, preferably under fluoroscopic X-ray. This procedure is limited because, among other limitations, it does not provide direct visualization of the discectomy site.
Other procedures have been developed which include arthroscopic visualization of the spine and intervening structure. U.S. Pat. Nos. 4,573,448 and 5,395,317 to Kambin disclose percutaneous decompression of herniated discs with a posterolateral approach. Fragments of the herniated disc are evacuated through a cannula positioning against the annulus. The '317 Kambin patent discloses a biportal procedure which involves percutaneously placing both a working cannula and a visualization cannula for an endoscope. This procedure allows simultaneous visualization and suction, irrigation and resection in disc procedures. These approaches seek to avoid damage to soft tissue structures and the need for bone removal through a channel. However, these approaches are limited because they do not address, for example, disc space distraction, disc space preparation and implant insertion into the disc space. The approach of the '317 patent also requires multiple entries into the patient, and the approach of the '448 patent does not provide for direct visualization of the working space.
Further examples of instruments and methods for performing spinal surgeries using minimally invasive approaches are found in U.S. Pat. Nos. 5,792,044 and 5,902,231 to Foley et al. The present invention is also directed to further improvements and techniques using a minimally invasive approach for performing spinal surgery.